Managed pressure drilling (MPD) wellbores through subsurface formations includes the use of a device known as a rotating control head or rotating control device (RCD) at a selected position above the top of the wellbore. The RCD includes a bearing and seal assembly that enables rotation of a drill string, and longitudinal motion of a drill string as the wellbore is drilled, while maintaining a fluid-tight seal between the drill string and the wellbore so that drilling fluid discharged from the wellbore may be discharged in a controlled manner. By controlling discharge of the fluid from the wellbore, a selected fluid pressure may be maintained in the annular space between the drill string and an exterior of the wellbore. Control of the discharge may be performed manually or automatically. One automatic system for controlling fluid discharge from the wellbore is described in U.S. Pat. No. 7,350,597 issued to Reitsma et al. and incorporated herein by reference.
Drilling, production and completion of offshore wells from a floating platform, e.g., a vessel, tension leg platform, etc. is conducted through a riser assembly which extends from the platform to the wellhead on the sea floor. The riser assembly includes a series of pipe sections connected end to end. Marine drilling risers provide a conduit through which materials may flow between the platform and a wellbore. While the platform from which the wellbore activities are being conducted is maintained as nearly as possible in the fixed position above the wellhead, there is some variation in this relationship, such that there is relative lateral and vertical shifting between the two. Accordingly, the riser assembly accommodates this relative movement between the platform and the wellhead as well as forces acting on the riser assembly from waves, currents and the like.
Marine managed pressure drilling using a riser or drilling fluid returns thus uses an RCD at a selected position along the length of the riser. FIG. 1 shows a conventional marine drilling system having an outer barrel 16 of a telescoping riser section coupled to the top of a fixed length of riser (not shown) that extends to a subsea wellhead (not shown). The telescoping riser section is supported by a tension ring 20 coupled to the outer barrel 16. The tension ring 20 is a type of buoyancy component for supporting at least part of the weight of the riser in a body of water. The tension ring 20 includes cables (not shown) that extend to the floating drilling platform 11 in order to transfer some of the buoyancy thereof to the tension ring 20 to support at least part of the weight of the riser in the body of water. An inner barrel 14 slidably, sealingly engages the interior of the outer barrel 16. A flex joint 12 and a diverter 10 are disposed at the top of the inner barrel 14. Thus, the length of the riser is able to be changed in order to compensate for heave of the drilling platform 11. The riser is also able to be moved laterally to compensate for lateral motion of the drilling platform 11. The tension ring 20 is disposed at a selected distance below the top 18 of the outer barrel 16.
FIG. 2 shows a system known in the art for marine managed pressure drilling. The system in FIG. 2 includes first and second inner barrels 14A, 14B, respectively, that sealingly, slidably engage with each other, where the second inner barrel 14B engages the outer barrel 16. In the system of FIG. 2, the outer barrel includes a top joint 16A that performs the function of slidably, sealingly engaging the inner barrel 14. An RCD 22 and an annular blowout preventer (BOP) 24 are coupled to the lower end of the top joint 16A, for example, by flanged couplings. A flow spool 26 is disposed below the annular BOP 24 to provide a flow path for drilling fluid exiting the well where a flow path in the riser above the RCD 22 is sealed by the RCD 22 when a drill string (not shown) is inserted therein. The tension ring 20 is disposed at a convenient position below the flow spool 26. The remainder of the lower barrel 16 is disposed below the tension ring 20. The remaining components of the system in FIG. 2 are similar to those shown in FIG. 1.
FIG. 3 shows another marine MPD system. In the system of FIG. 3, the RCD 22, annular BOP 24 and flow spool 26 are coupled to the bottom of the outer barrel 16, thus below the tension ring 20, which is affixed to the outer barrel 16 as previously explained. The system in FIG. 3 further includes a termination joint 28 disposed below the flow spool 26.
The marine MPD systems shown in FIG. 2 and FIG. 3 use extensive assembly and disassembly operations in order to service the RCD and the annular BOP. Further, testing the RCD and annular BOP may be performed after assembly of the riser system as shown in the foregoing figures.